* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: #000;
}
a {
  text-decoration: none;
  line-height: 50px;
  padding: 10px 40px;
  color: #fff;
  background-image: linear-gradient(
    to right,
    #03a9f4,
    #f441a5,
    #ffeb3b,
    #09a8f4
  );
  border-radius: 50px;
  text-align: center;
  font-size: 24px;
  font-family: Fira code;
  position: relative;
  z-index: 1;
  background-size: 400%;
}

a::before {
  height: 100%;
  width: 100%;
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  content: "";
  background-image: linear-gradient(
    to right,
    #03a9f4,
    #f441a5,
    #ffeb3b,
    #09a8f4
  );
  filter: blur(20px);
  z-index: -1;
  background-size: 400%;
}
a:hover {
  animation: sun 8s infinite;
}
a:hover::before {
  animation: sun 8s infinite;
}
@keyframes sun {
  100% {
    background-position: -400% 0;
  }
}
